I think the server doesn't allow us to send mass mailings. Fortunately most frequent visitors will not give up. The cache issue will solve by itself, but I'm not sure how long a web browser caches css files.

I sent Erwin a PM about this last night, mentioning that the display was OK in a couple of browsers but messed up in others. He suggested that a refresh should help: pressing Ctrl+F5 (instead of just pressing F5 or clicking on the 'Reload' button) did indeed solve the problem.

It has since occurred to me that the affected browsers were my default browser and another one that I use quite frequently. The unaffected browsers presumably didn't have any cached CSS, so they used the new CSS supplied by the server and therefore displayed the pages correctly without any intervention from me.